Hydroxy-functional acrylic resins having molecular weight (typically 5000 to 1000000) are valuable reaction intermediates for high-performance coatings. These resins are typically synthesized by copolymerizing hydroxyalkylacrylate or hydroxyalkylmethacrylates monomers or mixture thereof with other alkyl acrylate/alkyl methacrylate monomers such as butyl acrylate, butyl methacrylate, methyl methacrylate etc, along with styrene, methacrylic acid and suitable initiator. Since Hydroxyalkylacrylate/methacrylate monomers are fairly expensive, inexpensive ways to introduce hydroxyl functionality into acrylics while maintaining desired coatings performance is an area of interest.
In order to meet the basic objective of achieving economy and performance, polymer scientists have used vegetable oil or its derivatives with acrylics and some of such references are being mentioned here.
Use of Castor oil to modify thermosetting acrylic based coating compositions have been reported m U.S. Pat. No. 3,454,509 to impart flexibility, hardness and low baking schedule to the coating. This prior art relates to addition of small quantity of castor oil or its derivative into the coating recipe containing thermosetting acrylic co-polymer and cured with hexamethoxymethyl melamine cross-linker.
U.S. Pat. No. 3,454,509 describes the use of castor oil as a reactive flexibilizer (as an additive) where hydroxy group of castor oil does not react with interpolymer, instead it reacts with cross linker i.e. melamine formaldehyde and hence form the part baked coating. Castor oil in physical blending form doesn't react with interpolymer instead it acts as plasticizer. In another U.S. Pat. No. 5,432,221, hydroxy functional acrylic polymers have been reported which are compatible with castor oil. Such acrylic polymers find application in multi curable coating compositions comprising of hydroxy functional acrylic, polyisocyanate and castor oil. Use of castor oil provides flexibility and wetting to the polyurethane coatings prepared thereof but does not impart any hydroxy functionality to the acrylic polymers.
U.S. Pat. No. 5,432,221 describes use of acrylate resin based on petroleum based hydroxyl monomers (like Hydroxy Ethyl Acrylate/methacrylates etc.) which are highly reactive and hence to make it flexible castor oil and polyisocyanates have been used wherein the polyisocyanates react separately with acrylate resin and castor oil.
International patent No. WO 2010/100121 A1 discloses the synthesis of hydroxy functional oil polyol acrylic graft copolymers. This was accomplished by heating epoxidized vegetable oil and a hydroxy functional material in the presence at an acid catalyst to prepare hydroxy functional oil poyol and reacting the same with a mixture of ethylenically unsaturated monomer composition in presence of an initiator. The polymers prepared thereof were cured with suitable cross linker to prepare coating compositions for food & beverage packaging containers.
Epoxidized vegetable oil though a renewable material based polymer are entirely different in structure compared to castor oil grafted acrylate resin of the present invention. Examples cited in WO2010/100121 utilise, various commercial grades of epoxidized vegetable oil like Vikolox, Vikoflex 7170, Vikoflex 7190, Drapex 6.8, Drapex 10.4 etc having low iodine value (between 1-3) indicating almost no unsaturation and therefore leaves little scope of chemical grafting of monomers through unsaturation.
US2005/0203246 A1 discloses that ethylenically unsaturated vegetable oils like soya bean off and Linseed oil have been modified by the addition of an enophile or dienophile having acid, ester or anhydride functionality. The modified vegetable oil is then reacted with functional vinyl monomer to form a vegetable oil derivative. Such derivatives were found useful in forming latexes for coatings.
WO2012/131050A1 is about aqueous acrylic copolymerisate dispersions obtained of A) subjecting the monomer mixture comprising a) at least one hydroxyl functional vinyl, acrylate or methacrylate monomer and b) at least one acid functional vinyl, acrylate, or methacrylate monomer and c) at least one vinyl; acrylate, or methacrylate monomer that is not hydroxyl functional and not acid functional to free radical polymerization in the presence of d) 10-40 wt % based on the total weight of the monomers a), b), c) of at least one polyol selected from the group consisting of castor oil and castor oil based polyol derivatives having a number average molecular weight Mn of 600 to 1200 g/mol and an OH value of 160 to 400 mg KOH/g, yielding an acrylic copolymerisate composition, B) adding a neutralizing agent to the acrylic copolymerisate composition of step A), and C) dispersing the mixture resulting from step B) in water.
The dispersion of this prior art is thus prepared involving castor oil and hydroxyl acrylates like hydroxyl ethyl methacrylate, hydroxyl propyl methacrylates prepared in water miscible co-solvent that is water borne (aqueous) with sufficient carboxylic functionality/acid value to enable neutralization with suitable amines followed by dilution with water meant exclusively for waterborne coatings. The acid value is between 7 and 25 mg KOH/g.
WO2010/051346A1 is directed to a process of cross-linkable aqueous copolymer dispersion of a water dilutable copolymer A, comprising the steps of    1. polymerizing by radical copolymerization a) 5 to 64% by weight of a reaction product of at least one fatty acid having at least one ethylenic double bond and one hydroxyl group in the molecule with a polyalcohol having a hydroxyl functionality of 2 to 8 and b) 36 to 95% by weight of at least one additional unsaturated monomer b), wherein the at least one additional unsaturated monomer b) contains hydrophilic ionic groups and wherein the % by weight of monomers a) and b) are adding up to 100%, wherein the reaction product of at least one ethylenic double bond and one hydroxyl group in the molecule with a polyalcohol having a hydroxyl functionality of 2 to 8 is castor oil.    2. neutralizing the hydrophilic ionic groups of the copolymer A before and/or during dispersing or dissolving the copolymer A in an aqueous carrier.    3. dispersing or dissolving the neutralized copolymer A in an aqueous carrier, wherein the at least one additional unsaturated monomer b) is polymerized in presence of at least 20% by weight of the total amount of the reaction product a), thereby forming a copolymer A) having an acid number of at least 10 mg KOH/g solids.
This prior art thus teaches aqueous copolymeric dispersions prepared in water miscible co-solvent involving castor oil and a hydroxyl functional monomer with sufficient carboxylic functionality/acid value to enable neutralization with suitable amines followed by dilution with water which is meant exclusively for waterborne coatings. The acid value is high of 15-80 mg KOH/g solids.
As apparent from the above state of the art the provision of hydroxy functional acrylic copolymer utilizing renewable material as co-reactant as a source of hydroxyl functionality in the said resin with complete elimination or partial reduction in incorporation of hydroxy functionality through hydroxyl functional acrylic monomers is at a nascent stage and such renewable material based copolymers made available in the state of the art are water borne with high acid numbers required for aqueous dispersion for neutralization with amines to favour water dispersibility also involving acrylic acid and methacrylic acid as essential ingredients.
While the above cited arts describe the use of castor oil as an additive or other modified oils to be incorporated in hydroxy functional acrylics, there is a long felt need in the art for the provision of having renewable material derived hydroxy functional acrylic copolymer, wherein the renewable material would be a co-reactant for resin synthesis to economize, provide latitude and renewable component to the said resin and the coating compositions and other compositions attained therefrom. There is also a need in the art to provide for economical and durable clear/pigmented coatings which coating would have high renewable material content, high solid content and would be compatible with VOC (volatile organic content) exempt solvents to be solvent borne and could be prepared irrespective of the involvement of conventionally used petroleum based acrylic/methacrylic acid and irrespective of incorporation of hydroxy functionality through hydroxy functional acrylic monomers.